This invention relates to turbo machinery and, more particularly, to a combined water-wash and wet-compression system for the compressor of a gas turbine.
The compressor of a gas turbine requires periodic cleaning (sometimes referred to as water wash). One method of cleaning includes spraying droplets of cleanser into the inlet of the compressor. When this procedure is performed while the compressor is in operation, demineralized water is used and the droplets are sized to be large enough so that the drag forces are dominated by the inertia forces that tend to cause the droplets to impinge on the hardware of the compressor and provide the cleaning action.
It is also the case that a gas turbine compressor will require less power to operate at a given pressure ratio if intercooling is provided within the compressor. One method of providing intercooling includes spraying droplets of coolant into the inlet of the compressor. When the mixture of gas and water is compressed (generally referred to as wet compression), the temperature of the gas increases and provides the driving potential for evaporation. The evaporation of water cools the gas, and so acts as an intercooler. In this instance, coolant droplets are sized to be small enough so that the inertia forces are dominated by the drag forces that tend to cause the droplets to flow past the hardware of the compressor and travel into subsequent stages of the compressor where the droplets evaporate and provide the desired intercooling.
The current practice is to use separate systems for water washing and wet compression, each having their own set of controls and hardware.
An arrangement is desired that will reduce the cost and complexity associated with separate water-wash and wet-compression systems. This invention relates to a device or system that will provide a stream of large droplets for water wash that will impinge on the hardware of the compressor and provide the required cleaning of the compressor, as well as a stream of small droplets for wet compression that will not impinge on the hardware of the compressor, but will flow into the downstream stages of the compressor where the droplets will evaporate to provide intercooling.
In accordance with this invention, water droplets for both water wash and wet compression are supplied by dual-function nozzles within a single system.
In the exemplary embodiments of the invention, modifications are made to current water-wash manifolds, nozzles and controls that permit atomizing air to be selectively provided to each nozzle. In this way, when the atomizing air is introduced, the droplets are reduced to a size small enough to bypass the hardware of the compressor and flow into the downstream stages of the compressor, thus adding an intercooling function to the apparatus that previously provided only a water-wash function. When the atomizing-air function is not utilized, the droplets are sufficiently large for impacting and thus cleaning the compressor hardware. Two types of dual-function nozzles are described herein. In one embodiment, the nozzles may be of a commercially available twin-fluid type where a sheet of liquid is disturbed by a high-velocity sheet of air so as to eventually cause the sheet to disintegrate into ligaments and then into small drops when in the atomization mode. For water wash, the flow of atomizing air is halted, and the liquid sheet is simply broken up by ambient air into large droplets suitable for water wash.
In a second exemplary embodiment, small droplets for wet compression are supplied by a commercially available electro-mechanical atomizer. Electro-mechanical atomizers are a family of atomizers that includes pressure atomizers, rotary atomizers, electrostatic atomizers, ultrasonic atomizers, vibrating-capillary atomizers, windmill atomizers and flashing atomizers, for example. This family of atomizers produces small droplets when the pressure of the liquid is increased, when an electric field is applied, when gas is dissolved, or when some component of the nozzle is set into motion. An ultrasonic atomizer utilizing piezoelectric discs is described herein. In this device, the piezoelectric discs produce cyclic contraction and expansion that results in a pressure wave that travels axially along the nozzle, interacting with the liquid in the nozzle to cause a mist of small droplets to be ejected from the nozzle. On deactivation, the liquid droplets return to the larger size suitable for water wash.
Thus, in its broader aspects, the present invention relates to a combined water-wash and wet-compression system for a gas turbine comprising a compressor having an inlet defining a flow direction; a plurality of manifolds arranged in proximity to the inlet and arranged transversely of the flow direction; a plurality of dual-function nozzles connected to the manifolds, each dual-function nozzle adapted to supply, selectively, relatively small droplets for introduction into the compressor for intercooling, or relatively large droplets for impingement on components of the compressor for cleaning the components.
In another aspect, the invention relates to a gas turbine system including a compressor, a gas turbine and a generator, a combined water-wash and wet-compression system for a gas turbine comprising a compressor having an inlet defining a flow direction; a plurality of manifolds arranged in proximity to the inlet and arranged transversely of the flow direction; a plurality of dual-function nozzles connected to the manifolds, each dual-function nozzle adapted to supply, selectively, relatively small droplets for introduction into the compressor for intercooling, or relatively large droplets for impingement on components of the compressor for cleaning the components.
In still another aspect, the invention relates to a method of introducing a liquid into a compressor inlet for providing water wash for cleaning components of the compressor, and for providing wet compression for intercooling, the method comprising:
a) providing at least one array of nozzles capable of supplying both large and small droplets of the liquid to an inlet of the compressor;
b) operating the array of nozzles in a first mode where the droplets of liquid are sufficiently large to impinge on the components of the compressor in a cleaning function; and
c) operating the array of nozzles in a second mode where the droplets are sufficiently small to flow past the components of the compressor and into later stages of the compressor where the droplets evaporate for intercooling.